So this is one of those jobs that i go to now and again...it's not much fun.
I tried different methods of welding to the broken studs but nothing worked. I put the welder away and I will be drilling them all out.
So far i've done 2 ..yes just 2. I work up in 0.5mm increments from 3mm to 6.8mm then use a tapered M8 tap re thread the hole. They seem good and the bolts that came out screw in really well.
The drill guides I had made up work really well for getting the first 3mm hole done.
Here you can see.
I'm just going to take my time with this..no rush.